1. Field of the Invention
The present invention relates to a navigation apparatus for a vehicle in which a route is determined in an ordinary-road-preferential mode or a toll-road-preferential mode, and route guidance is provided based on the determined route. The present invention also relates to a navigation apparatus for a vehicle in which when priority is given to toll roads, proper interchanges are located during route determination.
2. Description of the Related Art
In a conventional navigation apparatus, upon input of a destination and enroute points, there is determined an optimum route that starts from the present position of the vehicle or a preset start point and reaches the destination after passing through the enroute points, and based on the thus-determined route, route guidance is provided by means of voice output and display.
In such a navigation apparatus, road map data is stored in a CD-ROM, and the road data is utilized for determination of an optimal route and creation of a map to be displayed on a display screen.
In such a case, road data for route determination is stored for each road section between intersections or between branch points. Specifically, there are stored information peculiar to each road section and information representing connections (links) between the road sections. The information peculiar to each road section includes a road length, a road width, and a road attribute. During route determination, a search cost is determined through use of these pieces of information. The road attribute indicates a road type that is determined based on the actual road; i.e., a highway, a national road, a prefectural road, or an ordinary road. Especially, toll roads such as a highway are regarded as special roads and are distinguished from other types of roads.
When route determination is performed through use of such a navigation apparatus, a user can select a toll-road-preferential mode, or an ordinary-road-preferential mode for route determination. When route determination is performed in the toll-road-preferential mode, the route determination is carried out after the search costs of toll roads are decreased relative to the case were the route determination is carried out in the ordinary-road-preferential mode. This technique realizes an improved route determination in which a route is determined so as to include a toll road or roads if possible when priority is given to toll roads, whereas a route is determined so as to avoid toll roads if possible when priority is given to ordinary roads. As described above, depending on a user's preference, the route can be changed to some extent.
Moreover, in the above-described navigation apparatus, when the vehicle deviates from a predetermined route during route guidance, a new route from the present position of the vehicle to the destination is determined automatically or in response to an instruction from the user, to thereby provide proper route guidance.
However, the above-described conventional navigation apparatus cannot satisfy the user in the following cases. When the user causes the navigation apparatus to determine a route in the toll-road-preferential mode, a route passing through a toll road or roads is determined. However, the user may feel that using the toll road or roads is not necessary, for example, in the case where a major road extends along the toll road or roads.
Also, when the user causes the navigation apparatus to determine a route in the ordinary-road-preferential mode, there is determined an improper route in some cases, for example, a route passing through an old road that is difficult to drive on while a newly opened toll tunnel or the like is avoided. In such a case, the user feels that the route passing through the toll tunnel or the like is preferable if the toll is not very expensive. Moreover, when the user travels to an unfamiliar destination, it may be difficult for him or her to determine whether the route determination is to be performed in the toll-road-preferential mode, or in the ordinary-road-preferential mode.
In the above-described cases, it is preferred that the selection of mode between the toll-road-preferential mode and the ordinary-road-preferential mode be carried out automatically unless there is a demand for route determination in which a route is determined such that toll roads or ordinary roads are excluded completely.
The accuracy of navigation apparatuses in detecting the present position has improved drastically; accordingly, the possibility that the user mistakenly deviates from the route due to a detection error of the present position has decreased. When the user deviates a road deviated from the determined route, the user may use the road intentionally due to some reasons. For example, when the user leaves a route that has been determined in the ordinary-road-preferential mode and then enters a toll road, if the navigation apparatus is in a mode for automatic redetermination, a new route is determined based on the present position of the vehicle, or the present position on the toll road. However, in the conventional apparatus, there is determined a route that leaves the toll road immediately and enters an ordinary road, because if an initial determination is conducted in the ordinary-road-preferential mode, the redetermination is also conducted in the ordinary-road-preferential mode.
In the above-described case, the user determines the initial route while giving priority to ordinary roads and then during travel the user changes the route to use a toll road. Such route change is often performed when ordinary roads on the route have heavy traffic and the user expects to require an extremely long time to pass through the traffic; i.e., when the user's intention has changed. Of course, the user can change the operation mode from the ordinary-road-preferential mode to the toll-road-preferential mode. However, the operation for switching the operation mode is troublesome.
There are opposite cases where the user determines the initial route while giving priority to toll roads and then during travel the user changes the route to use an ordinary road. Such route change is often made when the user obtains information indicating presence of a traffic jam or traffic regulation ahead on the toll road presently used and wants to avoid such a situation. In such cases, since the operation mode has been set to the toll-road preferential mode, a new route is determined to cause the driver to use the toll road again, so that the user's will or intention of leaving the original route is not reflected in the new route determination.
Moreover, in the conventional navigation apparatus, when route determination is performed in the toll-road-preferential mode, there is output a route which causes the driver to use an interchange which seems to be closest to the start point or the destination (see, for example, Japanese Patent Applications Laid-Open (kokai) Nos. 4-232812 and 5-341712).
However, in such a conventional navigation apparatus, when a route determination is performed in the toll-road-preferential mode, an interchange located in the direction opposite the direction of a destination that the user desires to go is sometimes selected because of the proximity of the interchange. In such a case, the user feels that the determined route is a long way around, an excess amount of fuel is consumed, and the driver is forced to turn the vehicle in the opposite direction, thereby making the maneuvering of the vehicle troublesome. Similar problems occur in the vicinity of the destination.